So, there seems to be a problem with that StageOne product: it only measures left leg power. Since the strain gauges will only see the longitudinal bending stresses, it can only measure the bending on the left side. Unclip from the left side, and you won't see any power.

There's a reason most crank based power meters are spider-base: the power ALWAYS goes through the spider. I remember seeing some BB-based ones, but I'd bet they'd see the same problems as this one would have

About the Aluminum only: make sense, as I would guess aluminum is more consistent in that you can calibrate on one crankarm, and, odds are, it'll be very similar on another crankarm. Not a materials guy, but I know there are some folks in the composites field here that could confirm or deny this lurking on the board.

Now, if they put out a pair of these, one for each arm, that might have a winner...

Since you are measuring the left side only, do you display just ones legs output?

From our testing we have found that there is not a large variation from a riders left to right leg while riding. We make the assumption that your right and left leg’s are doing the same amount of work and double the left leg’s power. So the number that you see while training is for both legs.

It will only make a few watts difference from another power meter, well within the typical 2% variance they all claim.

Either you will be stronger with your left or right leg, and the power numbers will be slightly higher/lower than a regular. But who cares really, everybody is one side dominate, and the point is using the power meter to improve your riding, it would be assumed it wouldn't matter whether you had a spider or not, you can benefit the same if used properly.

Also, I used one of these on a bike at the gym, it was the fatter boxier unit for fitness bikes. Must say, the thing was damn accurate and worked well.

For the money, and assuming you have aluminum cranks (WTF is that all about, still didn't understand that??), good value overall.

They absolutely won't maintain 2% accuracy doing left leg only. Measurements which have been reported with pedal-based systems have shown more variation than this, for example comparing high to low cadence, or when fatigued versus when fresh, or when pain starts creeping into one or the other knee, etc.

Another factor: acceleration-based cadence is challenging if you don't have a way to separate centrifugal acceleration from the bike bouncing up and down. I wonder how they make that work and how well it works, especially at lower cadences (for example, 40 rpm) on rough roads, especially since their accelerometers appear to be on an intermediate radius of the crank arm (where centrifugal acceleration is less than on the outer radius, for example at the pedal).

It's great to see the diversity of solutions being created, but I'm skeptical of how this one works on the road (stationary trainers are relatively easy).

I would be fine with it as a $200-300 entry level - it's certainly more useful than a PowerCal (which I think is just a marketing tool to sell a PT later). Of course, the market means that they're relatively cheap for a direct measurement device, but I'd class this as a good introduction to power or suitable for a casual user.

They may be a lot better than ergomo but the memories of 'ergomo watts' are still pretty fresh.

It really opens up the comparison opportunities though - could have SRM, Stages, PT, iBike,Vector/Polar and Brim in a grand PM shootout...

Some of you guys crack me up. Dimples on carbon wheels are an absolute necessity, despite the fact that golf balls and bike wheels are about as different as night and day.

And let's not forget the ceramic bottom bracket bearings, which save an estimated 450 watts on a 40kilometer time trial. That nonsense gets eaten up like chum around here, but the second someone mentions wanting a power meter that records power from both legs independently, all of a sudden I have to be told by those who say they don't need it that it isn't necessary for EVERYONE.

It's not about need, it's about preference. Power meter have been around long enough for someone to put out a decent and reasonably priced item that does what it should do without having to compromise on which crank side I need to calibrate.

Not very impressed with the effort being made in this field by manufacturers, especially since I've heard it being mentioned on this site the technology involved in making one is no more complex than that of a digital bathroom scale.

Power meter have been around long enough for someone to put out a decent and reasonably priced item that does what it should do without having to compromise on which crank side I need to calibrate.

Not very impressed with the effort being made in this field by manufacturers, especially since I've heard it being mentioned on this site the technology involved in making one is no more complex than that of a digital bathroom scale.

So technology is not about innovation rather than persistence, while I know a few engineering colleagues who try to take that approach it generally doesn't work well.

Having worked on measurement and instrumentation before on fusing sensor data, modelling sensor performance and writing and optimising Kalman filters. I can assure you it is a lot more complicated than a set of bathroom scales. More so if you consider that this is a product that has to operation in a hostile environment and require little / if any calibration during it's lifetime.

A power meter is still a niche product, the R&D investment, product development cycle and cost reflect this.

Having a CF poweremeter'd-crankarm available (specifically RED/Exogram) would be ideal for me personally, and if sales are strong I imagine that would be in development soon enough.

It seems that will not be the case unless someone solves (quoting the Bike Radar article) the``inherent problems with hysteresis associated with composite construction''and hence``the StageONE will only work with aluminum arms.''

Too bad, another powermeter that doesn't work with Campagnolo.

I wonder if the problem is the fixation of the sensor in the crankarm due to the different properties of carbon fiber or some sort of electro-mechanical coupling in the circuit due to the heat dissipated during the hysteretic cycle. If it's the second cause, It would be interesting to compare the errors due to this and due to total power calculation algorithm

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